1. Field of the Invention
Embodiments of the invention relate to a hard disk drive. In particular, embodiments of the invention relate to a hard disk drive comprising a clamp, and a balancing weight is coupled to the clamp.
This application claims priority to Korean Patent Application No. 10-2005-0114044, filed on Nov. 28, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
2. Description of Related Art
Hard disk drives (HDDs), which comprise both electronic and mechanical parts, are memory devices adapted to store data for later recovery by converting digital electric pulses into a magnetic field adapted for more permanent storage. HDDs are widely used as auxiliary memory devices in computer systems because HDDs allow relatively rapid access to a relatively large amount of data.
Recent increases in TPI (tracks per inch) and BPI (bits per inch) capabilities have generally improved the performance of contemporary HDDs. HDDs are thus being used in a broader range of applications. For example, a compact HDD having a diameter of 0.85 inches has recently been developed and is expected to be used in future mobile phones.
FIG. 1 is a perspective view of a conventional hard disk drive, and FIG. 2 is a cross-sectional view of a disk stack assembly of the hard disk drive of FIG. 1. Referring to FIGS. 1 and 2, a conventional hard disk drive 101 comprises disk stack assembly 110 comprising a plurality of disks 111 adapted to store data, and a head stack assembly (HSA) 130 adapted to read data from disks 111 while pivoting upon a pivot shaft 137 to move across disks 111. Conventional hard disk drive 101 further comprises a printed circuit board assembly (PCBA) 140, which is adapted to control the previously described elements of conventional hard disk drive 101. In PCBA 140, most circuit parts are installed on a printed circuit board (PCB). Conventional hard disk drive 101 further comprises a base 150 on which the previously described elements of conventional hard disk drive 101 are disposed, and a cover 160 adapted to cover base 150.
Disk stack assembly 110 comprises disks 111, a spindle motor 113 comprising a spindle motor hub 112 adapted to support and rotate disks 111, a spacer 117 disposed between two disks 111 and adapted to separate the two disks 111 from one another, a clamp 115 adapted to elastically press disks 111 between clamp 115 and spindle motor hub 112 to thereby fix disks 111 to spindle motor hub 112 (i.e., hold disks 111 fast to spindle motor hub 112), and a clamp screw 114 that passes through an installation hole 116 formed in clamp 115 and is screwed into (i.e., screw coupled to) a screw hole (not shown) formed in spindle motor hub 112. Clamp screw 114 presses clamp 115 so that clamp 115 will thereby fix disks 111 to spindle motor hub 112.
Imbalance occurs in a rotating system such as head stack assembly 130 or disk stack assembly 110 when there is a disparity between the center of gravity of the rotating system and the center of rotation for the rotating system. A static imbalance occurs in the rotating system when the previously mentioned disparity arises when the rotating system is not being rotated. A dynamic imbalance occurs in the rotating system when the previously mentioned disparity arises when the rotating system is rotating. An imbalance in a rotating system causes vibration and noise when the system rotates. In particular, in disk stack assembly 110, when there is a disparity between the cumulative center of gravity of disks 111 and the center of rotation for a rotational shaft 139 of spindle motor 113, a ball bearing or fluid bearing of spindle motor 113 may be damaged, which may reduce the reliability of conventional hard disk drive 101. Although there are many reasons for an imbalance to occur in disk stack assembly 110, an imbalance is mainly generated because elements such as spindle motor 113, disks 111, and spacer 117 of disk stack assembly 110 each have their own tolerance, i.e., the outer diameter of an upper portion 125 of spindle motor hub 112 of spindle motor 113, the inner diameter of each disk 111, and the inner diameter of spacer 117 each have their own length. That is, the imbalance is generated when the center of rotation for each element of disk stack assembly 110 (i.e., the center of rotation for the entire disk stack assembly 110) does not match the center of gravity of the entire disk stack assembly 110.
Many studies have been conducted in attempts to remedy the imbalance in disk stack assembly 110. For example, referring to FIG. 2, in disk stack assembly 110 of conventional hard disk drive 101, two disks 111 are pushed in opposite directions as indicated by arrows 118 and 119 to adjust the position of each of disks 111 with respect to the center of rotation for rotational shaft 139 (i.e., to bias each of disks 111) to improve the balance of disk stack assembly 110. A problem with this technique, however, is that it cannot be used for a hard disk drive comprising a single disk.
FIG. 3 is a cross-sectional view of a disk stack assembly 110a of another conventional hard disk drive. Referring to FIG. 3, in the conventional hard disk drive, a disk 111a and a spacer 117a are pushed in opposite directions as indicated by arrows 120 and 121 to adjust the positions of disk 111a and spacer 117a with respect to the center of rotation for rotational shaft 139a (i.e., to bias disk 111a and spacer 117a) to improve the balance of disk stack assembly 110a. FIG. 3 also shows a spindle motor hub 112a, a spindle motor 113a, and a clamp 115a. In the conventional device of FIG. 3, when using spacer 117a to improve the balance of disk stack assembly 110a, since changing the dimensions or volume of spacer 117a in the axial direction is strictly limited due to the characteristic(s) of spacer 117a, changing the dimensions, volume, or position of spacer 117a in the radial direction is unavoidable. Thus, the problem of reducing a data zone of disk 111a arises. In addition, when spacer 117a is omitted in an effort to reduce the cost of the hard disk drive comprising disk stack assembly 110a, the technique of adjusting the position of spacer 117a cannot be used.
Additional methods considered for balancing a disk stack assembly that has an imbalance due to the assembly of the corresponding hard disk drive are attaching an adhesive to the clamp, or screwing a balance weight to an installation hole of the clamp, wherein the installation hole is not occupied by a clamp screw. If an adhesive is attached to the clamp, the adhesive would be an additional part of the disk stack assembly.
The method of attaching the adhesive, however, may generate a contaminant in the hard disk drive and require a cleaning process. In addition, a special environment is needed to cure the adhesive, and the time needed to perform the process of curing the adhesive would extend the amount of time needed to assemble the hard disk drive.
Also, even when the method of screwing a balance weight into an installation hole that is not occupied by a clamp screw is used to compensate for a static imbalance in the disk stack assembly, a dynamic imbalance may still occur. In a dynamic imbalance, there is a disparity between the center of rotation for a rotational shaft of a spindle motor of the disk stack assembly and the center of gravity of the disk stack assembly when the hard disk drive is operated and the spindle motor is rotated after the hard disk drive is assembled. When the method of screwing a balance weight into an unoccupied installation hole is used to compensate for the static imbalance, it may be difficult or complicated to further compensate for a dynamic imbalance since the balance weight has been screwed into an installation hole of the clamp; and thus, the dynamic imbalance weight may need to be installed in the installation hole in which the balance weight has already been installed.